The Global Positioning System (GPS) is based on the fixed location base stations and the measurement of time-of-flight of accurately synchronized station signature transmissions. The base stations for the GPS are geo-stationary satellites and require atomic clocks for synchronization.
GPS has several draw backs including relatively weak signals that do not penetrate heavy ground cover and/or man made structures. Furthermore, the weak signals require a sensitive receiver. GPS also utilizes a single or narrow band of frequencies that are relatively easy to block or otherwise jam. The accuracy of the GPS system relies heavily on the use of atomic clocks, which are expensive to make and operate.
In addition, GPS utilizes a relatively slow update rate; on the order of once per second, which makes it ill suited for use in autonomous navigation of a vehicle. For example, a vehicle traveling at 10 kph would move about 2.75 m in a second. For an autonomous vehicle, significant changes in terrain or direction may occur in this distance, making an update rate of once per second much too slow.
Known triangulation methods are also numerical in nature, so (that no direct solution is readily available to find the location of the target. Rather, these open-form solutions provide only an initial guess and iterative numerical solution to estimate the location of the target. The resolution and accuracy of the location determination suffers accordingly. Further, using an open form solution in three dimensions is very difficult.
It has become increasingly desirable to have vehicles that are able to operate (e.g. move and/or carry out assigned tasks) without direct control from a human operator. Amongst other capabilities, such autonomous vehicles (AVs) have the ability to operate without direct control of a human and allow human operators to remove themselves from the vehicles. Alternatively or additionally, AVs can also permit the human operators to delegate repetitive tasks to the vehicle.
Often, these autonomous vehicles send signals to and/or receive signals from beacons for determining the autonomous vehicles' distance from and/or location relative to those beacons. As an example, U.S. Pat. No. 7,403,783 and U.S. Patent Application No. 2008/0234930, which are herein incorporated in their entireties by reference for all purposes, disclose a system of beacons and the navigation of a target or AV using those beacons.
Another example, U.S. Patent Application No. 2008/0262669, which is herein incorporated by reference for all purposes, discloses a controller for providing a vehicle with autonomous control and a method of providing path planning to an autonomous vehicle. Other examples of systems are disclosed in U.S. Pat. Nos. 7,110,881; 7,286,624; and 7,132,982, all of which are incorporated herein by reference for all purposes.
The signals sent between the AV and the beacons can experience interference from objects located between the AV and the beacons or otherwise and such interference can cause inaccuracy in distance and location determinations. As such, it is typically desirable for the determination of the AVs' distance from and/or location relative to the beacons to account for and/or minimize such inaccuracy. In the interest of overcoming some of the difficulties or drawbacks of prior AV locations systems or methods, the present inventions provides methods and systems for location of an autonomous vehicle, which alleviate inaccuracy in distance and locations determinations of AVs as well as path planning for the AVs.
While traversing a path, it is advantageous for an AV to efficiently range to selected beacons or base stations due to accuracy and time consideration. For example, in a scenario where there is a large multitude of beacons time constrains may prohibit an efficient measuring of ranges to each of the beacons. Moreover, due to non-line-of-sight, and/or excessive range (signal is too weak) it may also difficult for an AV to accurately range to a beacon. Therefore, it is desirable for the AV to know in advance which beacons it is desirable to range to so the AV can receive a response with the most accurate range information. The present invention provides a system and method for locating the position of an autonomous vehicle or target and methods of such location, by allowing select beacons to range to the target at a particular location.